Asymmetrical free piston motor compressor



Aug. 17, '1937. R. PATERAS PEscARA 2,090,424

' ASYMMETRIQAL FREE PISTON MOTOR COMPRESSOR Filed July 11, 1956 3 Sheets-Sheet l 3 J? 10 .22 'Z 10 2 23 J3 3 I 5 Z/mswfan life/my.

Aug. 17,1937. R. PATERAS PESCARA 2,090,424

ASYMMETRICAL FREE PISTON MOTOR COMPRESSOR Filed July 11, 1956 3 Sheets-Sheet 2 BLQN QQW I Aug. 17, 1937. R. PATERAS PEscARA 2,9 4

ASYMMETRICAL FREE PISTON MOTOR COMPRESSOR Filed July 11, 1936 a Shets-Sheet 5 Patented Aug. 17, 1937 UNITED STATES ASYIVIIVIETRICAL FREE PISTON MOTOR COIVIPBESSOR Raul Pateras Pucara, Paris, France Application July 11, 1936, Serial No. 90,236 In Belgium July 13, 1935 13 Claims.

This invention relates to internal-combustion motor compressor units of the free andopposed piston type, meaning thereby motor-compressors comprising motive pistons adapted to compress a gaseous medium without the interposition o rotating machine parts. It relates more particularly to units of this type comprising at least one compression stage, and stillmore particularly, to such units of the asymmetrical type, meaning thereby motor-compressors in which each compression stage comprises only one compressor cylinder and co-acting piston, as opposed td the symmetrical type, in which each compression stage comprises two identical compressor cylin- 5 ders and coacting pistons symmetrically disposed with respect to, and at opposite ends of, the motor cylinder. It also applies incidentally to motor compressors of the type described which are used to generate a power-conveying compressed gas to be subsequently used in a heat engine, such as a gas turbine.

The main purpose of my invention is to simplify the construction of said devices, and to reduce their weight, bulk and manufacturing cost.

The principal object of my invention is to provide a motor-compressor unit of the asymmetrical opposed piston type, as hereinbefore defined, in which the kinetic energy imparted to the motive pistons by the combustion of the fuel is transmitted to a single reciprocatingcompresslng assembly, directly by one of said motive pistons, that is through the 'medium of a rigid operative connection, and by the other motive piston,

through the medium of -a motion-reversing operative connection also adapted to synchronize the relative reciprocating motion of said two motive pistons, said compressing assembly comprising'at least one compressor piston co-acting with at least one compressor cylinder.

40 Another object is to provide a motor-compressorunit of the type described, in which said motion-reversing energy transmitting and synchronizing operative connection is adapted to perform its double function without the resulting strains induced therein exceeding by more than a small amount, those resulting solely from the inertia of the reciprocating parts.

A further object is to provide a motor-com pressor unit of the type described, comprising pneumatic energy storage or cushioning means for supplying at least part of the energy required for the return stroke of the motive pistons.

A still further object is to provide a motorcompressor unit of the type described, in which 5 said pneumatic energy supplying means are so dimensioned as to be adapted to simultaneously supply at least part of the energyfor the return stroke of motive pistons, and to so regulate the forces transmitted by said motio'n-reversingand synchronizing operative connection to the recip- 5 rocating compressing assembly that said forces will not exceed a relatively small function of the forces exerted on the motive pistons.

A still further object is to provide a single stage motor-compressor unit of the type described, in 10 which said pneumatic energy-supplying means consist in a single pneumaticcushioning cylinder and co-acting pistomthe compressor cylinder and co-acting piston being disposed at one end of the motor cylinder, and the pneumatic cushioning l5 cylinder at the other end of said motor cylinder, the capacities of said pneumatic cushioning cylinder and compressor cylinder being so related as to limit the forces transmitted by said motionreversing and synchronizing operative connection 20 to a relatively small fraction of the forces acting on the motive pistons.

A still further object is to. provide a three stage motor-compressor unit of the type described, in which the low-pressure stage and the pneumatic cushioning cylinder are disposed at one end of the motor cylinder, and the medium and high-pressure stages. at the other end of said motor cylinder, the capacities of said compressor stages and pneumatic cushioning cylinder being 30 so related as to limit the forces transmitted by said synchronizing operative connection to a relatively small fraction of the forces acting on the motive pistons,

A still further object is to provide a single or 35 multiple stage motor-compressor of the type described, also adapted to function as a power conveying gas generator, in which said pneumaticcushioning cylinder, located, in the single-stage type, on the opposite end of the motor cylinder 40 from that of the single compressor cylinder, and

. in the multiple stage compressor, at the same end of the motor cylinder as the lowest pressure compressor cylinder, is adapted to function at will as a two-stroke-cycle internal combustion engine, 45

the fuel injection therein being regulated, according to the delivery pressure of said motor-com pressor unit, in such a manner that, when said delivery pressure exceeds a given limit, the injec-' tion of fuel in said cushioning cylinder will be 50 reduced or stopped, said cushioning cylinder thereafter operating in the known manner as a. pneumatic cushion insuring the stability of the unit under reduced loads and down to no-load.

A still further object is to provide a motori compressor unit of the type described, in which the auxiliary pneumatic cushioning cylinder is replaced by a second motor cylinder co-acting with two opposed motive pistons.

5 Other objects and advantages of my invention will appear to one skilled in the art, from the following description, with reference to the accompanying drawings, it being understood, of course, that said description and drawings are given by way'of illustration, and should not be construed as limiting the scope of my invention.

In these drawings: Fig. 1 shows diagrammatically, in axial crosssection, a single-stage asymmetrical motor-compressor embodying my invention, and comprising a single compressor stage and a single auxiliary compensating pneumatic cylinder;

Fig. 2 shows schematically the linear and angular displacements of the kinematic synchronizing and motion-reversing operative connection between said motive pistons.

Figs. 3, 4, 5, 6, and '7 show diagrams of the forces transmitted by said synchronizing and motion-reversing connection.

Fig. 8 shows diagrammatically, also in axial cross-section, another embodiment of my invention.

Fig. 8a. shows a part of a modification of the form shown in Fig. 8.

Figs. 9 and 10 show various pressure-strok diagrams for this arrangement.

Fig. 11 shows, also in axial cross-section, a three-stage motor-compressor of the type described, comprising a single auxiliary compensating pneumatic cylinder.

Fig. 12 shows, also in diagrammatic axial cross section, a motor-compressor unit of the type adapted to operate as a free-piston power conveying gas generator, as hereinafter described,

40 also embodying my invention and comprising a single pneumatic energy accumulator adapted for use as a power-generating cylinder.

Fig. 13 shows, in diagrammatically axial crosssection, adouble motor-compressor unit comprising two distinct motor cylinders co-acting with two groups of oppositely reciprocating pistons.

Fig. 14 shows a detail of the synchronizing and power transmitting operative connection, as apfiled to the motor-compressor unit' shown in One of the essential characteristics of free piston engines is that they comprise no flywheel or other rotating parts, the reciprocating piston assemblies acting themselves as accumulators of energy in order to transmit said energy from the combustion chamber to the compressed gas reservoir. This type of transmission mechanism is. therefore adapted to transmit energy under exceptionally favorable conditions insofar as concerns regularity and efficiency, for the energy stored in kinetic form by the reciprocating assemblies under the action of the very high pressures of the motive gases during the combustion period 3 is transferred only gradually by said assemblies to the gaseous medium to be compressed, whereas in engines comprisingrotating crankshafts and I co-acting connecting rods driving a flywheel, the rapidly fluctuating forces to which the pistons are subjected are instantly and integrally transferred to the connecting rods and crankshaft whose function-it is to overcome the inertia of the flywheel and accelerate the same.

- mthermora wheri the motive parts of free piston engines consist of two pistons movable in opposite directions, it is necessary to synchronize said pistons through the medium of kinematic connections; and said connections must be of sufiicient strength to be able to transmit, in case one of the pistons should bind, all the energy imparted to the other piston. More particularly,-when said kinematic connections consist of connecting rods articulated to oscillating cranks, they may advantageously be used simultaneously to insure the synchronization of the reciprocating pistons, and as a safety device limiting the maximum length of stroke, in case the resistance of the air cushions should fail. Inthis last case, it may be shown that the connecting linkages may have to withstand considerable forces. The result is that said kinematic connections, if designed to operate both as a safety device and as synchronizing means, may be also used to transmit considerable amounts of power without the forces which they must transmit exceeding by more than a small amount the forces which they must be able to withstand when acting only as synchronizing and safety devices. It may thus be shown that, when the power transmitted by said connections equals one half of that generated in the motor cylinder, which is the case in motor-compressors having two motive pistons and only one compressor piston, the

forces transmitted by said kinematic connections may be of the order of one sixth to one tenth of the maximum forces'exerted on the pistons.

When the pneumatic energy storage means, in accordance with my invention, are located and dimensioned as specified hereinafter, the forces transmitted by said connections maybe soreduced as not to exceed the maximum strains to which they are normally subjected in symmetrical motor-compressors simply in overcoming the inertia of reciprocating parts, although they transmit no useful work in said symmetrical units. To this end, in accordance with one of the preferred forms of my invention, the engine pore tion of the unit consists of a motor cylinder l,

within which reciprocate in opposite directions two axially slidable motive pistons 21, and 2:,

piston 21 being rigidly connected with at least one compressor piston 3 co-acting with at least one compressor cylinder 4, and piston 22 being rigidly connected with the auxiliary piston 5 of the pneumatic cushioning means 6.

The piston assemblies 21-4 on one hand, and h on the other hand, are designed of exactly the same mass, in order to balance the machine, said masses being computed so as toadapt said assemblies to store in kinetic form the expansive energy of the burnt gases and to surrender the same progressively to the gaseous medium to be compressed. Part of said power is thus transferred directly to said gaseous medium by the assembly 21-4, and all or part of the energy stored in the assembly 21-! may be transmitted to the assembly '21-; by the kinematic connections consisting,'for example, of connecting rods I01 and II: and cranks II.

From extreme angular positions of the connecting rods I01 and I0: and of cranks H, as indicated in Fig. 2, may be computed the strains due to inertia which are transmitted by the reciprocating assemblies to said kinematic connections (see curve A B C D in Fig. 3).

Itmaybeseen that, duringtheflrstpart AB of the stroke, said connections must withstand a powerful force due to the acceleration of the reciprocating assemblies, whereas. during the second part B C of the stroke, thelnertia eifects are small; and finally, during the last part C D of the stroke, the acceleration of the reciprocatingparts reverses the forces transmitted by said connections.

For certain volumetric and manometric characteristics of compressor 4 and cushioning cylinder 6, corresponding to equal forces exerted at the outer dead centers on pistons 3 and 5, the diagrams shown in Fig. 4 (M N P Q for the compressor cylinder and M P for the pneumatic cushion) indicate the total pneumatic forces to which are subjected pistons 3 and 5'during the complete cycle of the unit (force fc on piston 3 and he on piston 5).

It may be seen that, during the working stroke, the compressor piston 3 is subjected to forces which are superior to those exerted on piston 5 of the auxiliary cushioning cylinder 6, and

that, on the contrary, during the return stroke, the piston 5 is subjected to greater forces than the piston 3. The difference between these forces (that is, the difference between corresponding ordinates in the diagram) is transmitted by the kinematic connections.

The diagram of Fig. 5 shows the differential strains at diflerent points of the working stroke (m n r) and of the return stroke (1' Q1 m) The superposition of the forces indicated in the diagrams of Figs. 3 and 5 gives the resultant forces to which the kinematic connections will be subjected in all their positions (curve I J K L 0 J I). It is seen that, in the case under consideration, the total forces to which are subjected said connections are relatively small andmay even never exceed the maximum due to,

the inertia eifect for which the kinematic connections have been designed. Said connections are therefore adapted to transmit the difference between the resisting forces produced by the '40 compressor 4 and the auxiliary cylinder 6.

-In general the kinematic connections are designed to transmit forces greatly in excess of those due to inertia; therefore the manometric and volumetric conditions of compressor 4 and of auxiliary cylinder 6- may be chosen such that the power transmitted by said kinematic con nections will, on the average, be very low, and

the maximum force at the outer dead center may be allowed to exceed slightly that due to inertia.

For example, as shown in Fig. 7, the auxiliary compensating cylinder 6 may be designed so that the maximum differences between the forces exerted on compressor piston 3 (M N P Q) and auxiliary piston 5, (M P M) will be substantially equal (differences indicated by curve 111, in, 213). For example, for adelivery pressure of the compressor equal to 7 atmospheres, if the ratio between the diameters of compressor cylinder 4 and auxiliary cylinder 6 be made equal to 1.15, the maximum force transmitted from one piston assembly to the other will only be about 550 pounds, whereas the maximum force exerted on the motive pistons will exceed 5,000

5 Pounds. I

In another embodiment of my invention illustrated in Fig. 8, the power transferred by the kinematic connections and the maximum strain to which they are subjected may be further reduced by feeding the auxiliary pneumatic cylin-' der 6 at a pressure higher than atmospheric pressure, for example, by connecting said cylinder to the delivery of the compressor at or near the inner dead center..

It may be seen by the diagram of Fig. 9 that the maximum difference between the forces acting respectively on pistons 3 and- 5 may be very example, by locating the connection between" cylinder 6 and the delivery of the compressor at a suitable point of the stroke of piston 5 as shown in Fig. 8a; in this manner the maximum differences n and 122 may be made substantially equal, as shown in Fig. 10. 4

In muiti-stage motor-compressor units such as that illustrated, by way of,example, in Fig. 11, in accordance with my invention, I locate the auxiliary compensating cylinder 6 at the same end of the motor cylinder as the low-pressure compressor cylinder 41, and adjacent to the same. For example, if said unit comprises 3 stages, the low-pressure stage and the aux iliary compensating cylinder are placed at one end of said motor cylinder, and the intermediate and high-pressure stages 42 and- 43 at the other end.

Contrary to the known practice heretofore, which consisted in balancing the forces acting on the respective .reciprocating assemblies by suitably choosing the volumetric and manometric ratios of the different stages, I prefer to retain for said stages the normal ratios corresponding to the maximum compressor efliciency (that is pressure ratios in geometric progression); and, in accordance with my invention, I dimension the auxiliary compensating cylinder 6 so as to adapt it to reduce the forces transmitted by the kinematic connections.

Although part of the power generated is transmitted by said kinematic connections, it is well known that the-mechanical efliciency of this type of transmission is excellent so that the overall efficiency of the motor-compressor unit is higher than if the volumetric and manometric ratios of the diiferent stages had been specially chosen to reduce to a minimum the forces transmitted by the kinematic connections.

In any case, the elements of the kinematic connections transmitting forces, however small the latter may be, may advantageously be disposed symmetrically with respects to the longitudinal plane of symmetry of the unit,.in order to avoid the formation of torsional couples.

Contrary to the arrangement generally adopted in symmetrical motor-compressor units, wherein the connecting rods articulated to two symmetrical cranks are crossed, in asymmetrical units of the type under consideration, I prefer to articulate symmetrical connecting rods such as I01. and I 02, in pairs, to a common axis l2- to which they may advantageously be rigidly connected as shown in Fig. 8, said axis revolving in long bearings formed integrally with the' piston assemblies. Each pair of rods thus forms with the axis [2 a rigid frame which makes it possible to reduce, and even to eliminate, sliding guides.

It is also possible in accordance with my invention, to impart to the respective piston assemblies reciprocating displacements of unequal but proportional amplitudes. I attain this end by making said assemblies of different masses,

In the casewhere the strokes of the piston assemblies are different, I prefer to impose the longest stroke to the assembly which comprises the hottest of the two motive pistons, that is, the motive piston closest to the exhaust ports, in order to intensify the cooling influence of the cylinder walls onsaid piston.

In motor-compressor operating on the twostroke cycle, it is necessary to provide, in addition to the energy-absorbing capacities 4 and 6, at least one scavenging pump, which pump may advantageously consist, as in Fig. 1, of the rear end of the compressor cylinder 4, limited by the inactive face of piston 3, forming a'chamber l5 in which air may be compressed on the inward stroke of piston 4 and fed into space 9 around the motor cylinder. It is evident that,

in this case, the energy absorbed by the'scavenging compressor is deducted from that available for the main compressor.

It is also possible, as shown in Fig. 1, to use part of the scavenging air to feed the auxiliary compensating cylinder 6, said air being introduced in said cylinder in any suitable manner; for example, by means of slots I! cut in the rigid connection between motive piston is and auxiliary piston 5; or by such means as duct 18 or its equivalent when the piston 5 is at the inner dead end of its stroke, scavenging air may flow from space 9 through slots I1 and duct ll into space 6.

In the special embodiment of my invention 11- lustrated in Fig. 12, the pneumatic cushioning cylinder 6 is adapted to function at will either as an ordinary energy storing compensating device, or as a power-generating two-stroke-cycie internal-combustion engine cylinder. To this end, said cylinder 6 is provided with a scavenging and combustion air intake 21 and valve 22, fuel injection means 23 and exhaust ports 24.

In this embodiment, I have also shown a motor-compressor unit adapted to the particular function of generating a gaseous medium under pressure and at relatively high temperature, which gaseous medium is to be subsequently used to operate a heat engine of. any suitable type,

such as, for example, a gas turbine. This special type of motor compressor I prefer to call a free and opposed piston power-conveying gas. gener-- is made double acting, and delivers the air com-.

pressed intothe storage reservoir I formed by the closed casing. At the end of the working 5 stroke, the motive pistons uncover the intake ports I!- and exhaust ports l9". The air stored under pressure in casing I penetrates into the motor cylinder l and passes out by the exhaust manifold 20, entraining the exhaust gases, the 'mixture of compressed air and exhaust gases at high temperature being subsequently expanded in the heat engine.

Insofar as concerns the auxiliary pneumatic cylinder 6, when it functions as a combustion engine cylinder, the compressed air from casing I passes through said cylinder 6 at the end of the working stroke, sweeping the burnt gases out through the exhaust manifold, where they mix with the exhaust from the main motor cylinder.-

In Fig. 13, I have shown still another embodiment of my invention, wherein the auxiliary pneumatic compensating cylinder is discarded and replaced by a second free piston motor unit of similar design to that of the first motor unit.

and connected therewith in tandem combination by suitable synchronizing and power transmitting kinematic connections, which are illustrated diagrammatically in Fig. 14, said kinematic connections being adapted to transmit all or part of the power generated in both motor cylinders to one single compressor piston 3.

The combined tandem motor unit comprises two motor cylinders l and 26, each co-acting with two opposed pistons, 2 and 2 in the first cylinder, and 21 and 28 in the second. Piston 2 is rigidly connected to piston, and motor pistons 2 and 21, and compressorpiston 3 are interconnected by means of the afore mentioned kinematic linkages consisting of connecting rods I0 I0 I01", I02", co-acting with cranks II and II. Said kinematic system is shown in Fig. 14 in skeleton form, that is omitting the motor units. The linkage system is articulated at two fixed points I and II, abreast of the two centers of the motor cylinders l and 26.

It shouldbe understood that I do not wish to -'be limited to the structural details described and her, said last means being also asymmetrically disposed in such a manner that the power, that is to be transmitted by the synchronizing linkage from one end of the internal combustion engine compressor to the other end thereof, produces a strain in the synchronizing linkage which is at most about equal to the maximum strains to which the synchronizing linkage is subjected under the action of the inertia forces even without transmission of power.

2. A single stage internal combustion engine compressor according to claim 1, said last means comprising a single compensating cushion arranged at one. end of the internal combustion engine compressor, the compressor cylinder at the end opposite the compensating cushion serving for the production of air for use.

3. A muiti-stage internal combustion engine compressor according to claim 1, said last means comprising a compensating cushion at the same end as the compressor cylinder of the lowest pressure stage, .and a plurality of compressor cylinders of higher compressor stages arranged at the opposite end of the compressor.

4. A single stage internal combustion engine compressor according to claim 1, said last means comprising a single compensating cushion arranged at one end of the internal combustion engine compressor, the compressor cylinder at the end opposite the compensating cushion serving for the production of air for use, said compensating cushion being so proportioned that'the maximum differences between the pressure loads, which act on the piston oi the cushion and on the 2,090,424 piston of the compressor cylinder are approximately' equal.

5. An internal combustion engine compressor according to claim 1, in which the initial pressure in the compensating cushion is above the surrounding pressure.

6. An internal combustion engine compressor according to claim 1, in which the pressurein the cushion is, during a first part of the stroke, kept constant at a value above the external pressure and then rises.

'7. An internal combustion engine compressor.

according to claim '1, inwhich the synchronizing linkage comprises two linkage portions which lie on the two sides of the compressor and each of which comprises a rocking lever pivoted about a stationary axis and two connecting rods connecting the rocking lever with the opposed pistons, the connecting rods of the two linkage portions lying parallel to each other in all positions.

8. An internal combustion engine compressor according to claim 1, in which the synchronizing linkage comprises two linkage portions which lie on the two sides of the compressor-and each of which comprises a rocking lever pivoted about a stationary axis and two connecting rods connecting the rocking lever with the opposed pistons, I

the connecting rods of the two linkage portions lying parallel to each other in all positions, the

corresponding piston, so that each pair of connecting rods forms a rigid frame with the corresponding axle.

' 9. An internal combustion engine compressor. according to claim 1, in which the oppositely reciprocating free pistons perform strokes of different length and are made of materials of diflerent specific gravities.

10. An internalcombustionengine compressor according to claim 1, in which the oppositely reciprocating free pistons perform strokes of dlflertionaryaxis and havingunequal arms.

chronizing linkage being rotatable about a sta- 12. An internal combustion engine compressor 1 according to claim 1, in which the compensating cushion mean'sis capable of operating as an internal combustion engine, cylinder. I

13. An internal combustion engine compressor according to claim 1, in which the compensating cushion means comprises a second motor cylinder with two co-acting opposed motive pistons, and

a synchronizing linkageconnecting said last motive pistons to the first motive pistons and to said compressor pistons.

. RAUL PATERAS PESCARA. 

